The use of very thin microchips has gained importance in the development of flexible electronics and the integration of chips in printed circuit boards. Ultra-Thin Chip Packaging (UTCP) technology is one example of newly developed technologies which include fabrication and integration methods of these thin chips. Other technologies which benefit from these thin chip technologies are for example micro-LED displays or high-density electronics. Regardless of the application, the thin chips are manipulated in a plurality of process steps, including the bonding of the chips to a larger substrate. When microchips are thinned down to ultra-low thickness (<50 micron) they become flexible and relatively fragile and are hard to manipulate using regular (vacuum-based) equipment used in microfabrication. A reliable approach for handling these thin chips is to attach them to a thick holder, carrier (carrier substrate), or carrier chip using a temporary adhesive. This way these thin chips can be handled as if they were microchips of conventional thickness and without special equipment being required.
A conventional way of getting the thin chips attached to a carrier or holder is by attaching a substrate with microchips to a carrier substrate provided with a film of temporary adhesive and subsequently, after attachment, thin down the microchips. This approach, however, has several drawbacks. For example, it is desired to have a low total thickness variation (TTV) of the thinned microchips population. However, when the microchips substrate is thinned while being bonded to a carrier substrate, the TTV of the carrier substrate adds up to the TTV of the temporary adhesive and the TTV of the thinning process, thus resulting in an increased final TTV of the thinned microchips population.
Thinning of chips while the chips are supported on an auxiliary substrate followed by the transfer of the thinned chips to a stiff carrier has also been described, for example, in U.S. Patent Application Pub. No. 2008/003780. In this document, however, the transfer of the chips to the carrier involves the bonding of the carrier directly to the thinned side of the chips while the chips are attached to the auxiliary substrate. This method allows only a single orientation of the chips with respect to the carrier, commonly called “face-up orientation.”